From: "skatkov (Stanislav (Stas) Katkov) via ruby-core" <ruby-core@...>
Date: 2025-05-25T14:51:40+00:00
Subject: [ruby-core:122289] [Ruby Bug#21372] Ruby is passing clang specific flags to GCC 15 and native gem doesn't build.

Issue #21372 has been reported by skatkov (Stanislav (Stas) Katkov).

----------------------------------------
Bug #21372: Ruby is passing clang specific flags to GCC 15 and native gem doesn't build.
https://bugs.ruby-lang.org/issues/21372

* Author: skatkov (Stanislav (Stas) Katkov)
* Status: Open
* ruby -v: ruby 3.4.4 
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
Fedora 42 has ompilation errors while running `gem install extlz4`.

```sh
At top level:
cc1: note: unrecognized command-line option ���-Wno-self-assign��� may have been intended to silence earlier diagnostics
cc1: note: unrecognized command-line option ���-Wno-parentheses-equality��� may have been intended to silence earlier diagnostics
cc1: note: unrecognized command-line option ���-Wno-constant-logical-operand��� may have been intended to silence earlier diagnostics
make: *** [Makefile:251: blockapi.o] Error 1

make failed, exit code 2

Gem files will remain installed in /home/sk/.local/share/mise/installs/ruby/3.4.1/lib/ruby/gems/3.4.0/gems/extlz4-0.3.4 for inspection.
Results logged to /home/sk/.local/share/mise/installs/ruby/3.4.1/lib/ruby/gems/3.4.0/extensions/x86_64-linux/3.4.0/extlz4-0.3.4/gem_make.out
```

I have submitted a ticket with a gem, but I have hunch that this might not be an issue with a gem, but rather a ruby compatibility issue with the new GCC (15).

@see https://github.com/dearblue/ruby-extlz4/issues/6

I have very little experience with C and how compilation works. But as far as I can understand, ruby was compiled with clang and is now passing some CLANG specifics flags to GCC 15 during native gem compilation - this causes a compilation error.

```sh
ruby -rrbconfig -e 'puts RbConfig::CONFIG["warnflags"].split(/\s+/).grep(/-Wno-/).sort'                                                                               
-Wno-cast-function-type
-Wno-constant-logical-operand
-Wno-long-long
-Wno-missing-field-initializers
-Wno-overlength-strings
-Wno-packed-bitfield-compat
-Wno-parentheses-equality
-Wno-self-assign
-Wno-tautological-compare
-Wno-unused-parameter
-Wno-unused-value
```

```
ruby -rrbconfig -e 'system RbConfig::CONFIG["CC"], "--version"'                                                                              
gcc (GCC) 15.1.1 20250521 (Red Hat 15.1.1-2)
Copyright (C) 2025 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
```

All my attept to overwrite compiler to use clang don't work either. I tried the following:

```
gem install extlz4 -- --with-cc=clang
CC=clang gem install extlz4
CC=/usr/bin/clang gem install extlz4 
```


## System
os: fedora 42
ruby: ruby 3.4.4 (2025-05-14 revision a38531fd3f) +PRISM [x86_64-linux] (but also tried it with 3.3.8, with no success)
gcc: gcc (GCC) 15.1.1 20250521 (Red Hat 15.1.1-2)

## Workaround
I run the following script and then it's possible to complete "bundle install" process.
https://gist.github.com/skatkov/df4db6f8b76e58fc8eefaa92592f2c1a



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